This invention relates to control mechanisms for motor vehicle engine operation and more particularly to systems for limiting the speed of the motor vehicle. The device is particularly useful for limiting the operating speed of diesel engine powered motor vehicles to a preset maximum value.
A speed limiter or governor limits the speed of the vehicle to a predetermined maximum. Speed limiting is typically accomplished by either a fuel bypass, a shutdown lever, or engine oil pressure control means.
Speed limiting systems are being used with increased frequency in the trucking industry by fleet owners for reasons of economy and safety. Speed limitation reduces the amount of fuel consumption during vehicle operation. Speed limitation also minimizes overall vehicle maintenance and particularly that required by the engine. Further, speed limitation increases vehicle operating safety through adherence to posted speed limits. This is a particularly important result for buses and motor coaches. Additionally, through adherence to posted speed limits, speed limiting systems help to maintain good operator driving records. Finally, speed limiting systems may provide added operator comfort and convenience through automatic maintenance of a preset maximum speed.
In the past, speed limiter devices have been used and proposed to limit the speed of motor vehicles, and some of these prior art devices are usable for diesel powered vehicles including trucks. However, these devices are generally complex, difficult to construct and install, and are inefficient and often unsafe to use. Specifically, some prior art devices are susceptible to manipulation by the operator to exceed the preset maximum speed limit. This practice, referred to as "teasing", involves repeatedly accelerating and decelerating the vehicle by depressing and releasing the accelerator pedal. These prior art devices have a long lag period before regaining control of the speed. This allows the vehicle speed to overshoot the speed limit momentarily, thereby increasing the average speed of the vehicle over the cycle of teasing. Such practices are inherently unsafe.
Some prior art devices are ineffective at limiting the vehicle speed to the preset maximum, particularly under windy weather conditions, heavy loads, steep grades or fast acceleration. These devices cause the vehicle to surge under these conditions. The surge phenomenon is both uncomfortable for the operator and unsafe.
Other prior art governor devices provide rough and inaccurate speed limitation which results in disconcerting speed variations. Such variations lead to operator dissatisfaction and rejection of use of the device.
Despite the need for a speed limiter device in the art which provides efficient and reliable speed limitation for motor vehicles, particularly diesel powered vehicles, which is simple to manufacture, install and use, and which overcomes the limitations and problems of the prior art, none insofar as is known has been proposed or developed.
Accordingly, it is an object of the present invention to provide a speed limiting device which reliably adheres to a predetermined maximum under a variety of weather, load, grade and acceleration conditions. It is a further object of the present invention to provide a speed limiter which is not susceptible to overshoot and droop. It is another object of this invention to provide a device which yields smooth and substantially imperceptable speed limitation. Also, it is an object of this invention to provide a speed limiter which is compact, unitary and easy to manufacture, install and maintain.